Vacuum pumps of the type referred to are generally mounted to the rear end portion of the electric generator for motor vehicles and the construction thereof will be described in conjunction with FIGS. 1 and 2.
Reference numeral (1) designates a rear bracket for an electric generator used with a motor vehicle and (2) designates a shaft supported by said rear bracket (1) through a bearing (3) and driven by an engine not shown. Reference numeral (4) designates a rotor A fixed to said shaft (2) through the spline fitting. Reference numeral (5) designates a housing having a inner cylindrical peripheral surface eccentric from the centers of said shaft (2) and said rotor A (4), (6) a plate put between said rear bracket (1) and said housing (5) to constitute a pump operating chamber (7), and (8) a mounting bolt for fixing said housing (5) and said plate (6) to said rear bracket (1). Reference numeral (9) designates vanes radially inserted into said rotor A(4) to be slidable in the diametric direction. Reference numerals (10) and (11) designate packings for keeping the airtightness of junction surfaces between said rear bracket (1) and the plate (6) and between said plate (6) and the housing (5), (12) an oil seal fixed to said bracket (1) and contacted by the periphery of said shaft (2) to keep the airtightness of the pump operating chamber (7), and (13), (14) and (15) a suction port, an exhaust port and an oil supply port which are provided on said housing (5) and connected to a vacuum tank (or a pressure accumulating portion of a master bag), an oil pan and an oil pump respectively, which are not illustrated. Reference numeral (16) designates a rotor B fixed to the shaft (2) to hold a field winding for the electric generator and (17) is a stator for holding an armature winding. Reference numeral (18) designates a front bracket constituting an outer frame of the electric generator with the rear bracket (1), and a bearing (19) is fixed to this front bracket (18) and rotatably journals the shaft (2). Reference numeral (20) designates a pulley fixed to the shaft (2) to receive the transmission of the rotation from the engine.
Regarding the operation, a description will now be made.
First with respect to the vacuum pump, when the rotation of the engine is transmitted to the pulley (20) by a belt to rotate the shaft (2) in the direction of the arrow, the vanes (9) spring outwardly by means of a centrifugal force caused on the vanes to be rotated while sliding along the inner wall of the housing (5), thereby to draw air from within the vacuum tank (or the pressure accumulating portion of the master bag) and exhaust it through the exhaust port (14) to perform the pumping operation. Also, an oil supplied to the interior of the housing (5) through the oil supply port (15) effects the lubrication of a sliding surface between the vanes (9) and the rotor (4) and is exhausted to the oil pan through the exhaust port (14).
With respect to the electric generator, an alternating current is induced on the stator by cutting a magnetic field generated from the rotor B(16) by means of the rotation of the shaft (2). This alternating current is rectified to a direct current which flows into a charging circuit on the side of a car body.
The electric generator for motor vehicles is generally belt-driven by an engine for a motor vehicle to be used with the number of rotations equal to about twice that of the engine in view of the power generation characteristic thereof. Thus regarding the vacuum pump directly connected to the generator, it is also used with the same number of rotations as the generator. For this reason, it is used according to the abrupt acceleration and deceleration from a range of low rotations (about 1000 rpm) to a range of high rotations (about 12000 rpm) and also the vacuum pump is continually being operated during the operation of the engine. Thus, the components constituting the vacuum pump have been previously required to have the durability and shock resistance with respect to the range of high rotations and long service resulting in an expensive device. Also, since the electric generator is driven through the belt, there has been the disadvantage that a vacuum cannot be obtained because the belt is broken to stop the vacuum pump.